The present invention relates generally to the use of robotic manipulators for lifting objects and particularly to the use of machine vision systems to aid in locating such objects.
In a wide variety of industrial applications, powered mechanical manipulators are used to lift and move objects from one place to another. When a powered mechanical manipulator is adapted to respond to a signal input (i.e., adapted for automatic operation) the powered mechanical manipulator is referred to as a xe2x80x9crobotic manipulator.xe2x80x9d Examples of such powered mechanical manipulators include forklifts, backhoes, jib cranes, gantry cranes, master-slave manipulators, and pick-and-place robots. In all applications of powered mechanical manipulators, the location of a target object to be lifted must be known to an accuracy high enough to ensure a successful lifting operation.
In one class of applications, such as, for example, automated circuit board assembly using a pick-and-place robot, location information is conventionally maintained by using a precision feed mechanism to accurately deliver target objects to known locations. An opportunity exists, in some instances of this application class, to gain economic advantage by replacing the expensive precision feed mechanism with a less expensive coarse feed mechanism combined with an automated target object location measurement system.
Similarly, in another class of applications, such as, for example, moving steel slabs in a steel mill using a gantry crane, location information is conventionally maintained by using a human operator to visually acquire target object locations. An opportunity exists, in some instances of this application class, to gain economic advantage by adapting the gantry crane for automatic operation and replacing the human operator with an apparatus for locating target objects.
The opportunities described above are addressed, in one embodiment of the present invention, by a system for lifting objects comprising: a Cartesian manipulator; a machine vision system adapted to acquire video images of the objects to be lifted; and a control processor adapted to process the video images and provide position command signals to the Cartesian manipulator.
The opportunities described above are further addressed, in another embodiment of the present invention, by an apparatus for locating a polygonal object comprising: a machine vision system for acquiring a video image of the polygonal object, at least one component of the machine vision system being disposed on a component carrying link of a robotic manipulator; an edge point locator for locating, in the video image, a new edge point corresponding to a respective edge of the polygonal object; an edge point accumulator for incorporating the new edge point into a historical point set; an edge line computer for computing a plurality of edge lines from the historical point set; a polygon center computer for computing a polygon center from the edge lines; and a manipulator command generator for commanding the robotic manipulator to move an end effector toward the polygon center by moving the component carrying link.
In some instances, it is also desirable, especially at the onset of lifting, to detect whether an object is tilted with respect to the horizontal. In another embodiment of the present invention, detection of tilt is addressed by an apparatus for detecting a tilted object comprising: a critical angle estimator for estimating a critical angle from a video image; an angle differencer for differencing the critical angle from the reference angle of a reference ray to yield an error angle; and an angle tolerance comparator for comparing an absolute value of the error angle to an angle error tolerance.